1. Field of Invention
The invention relates to a coordinate positioning machine such as a machine tool, inspection robot, or coordinate measuring machine. Coordinate positioning machines include a table for supporting an object upon which the machine is operating, and an arm movable relative to the table, typically with three linear degrees of freedom, which carries an operating module such as a cutting tool, an inspection probe, or a welding arm, for example.
2. Description of Related Art
Conventional coordinate positioning machines support the movable arm either, in the case of a robot, by a plurality of serially mounted rotatable joints, or, in the case of a machine tool and coordinate measuring machine, on a plurality of serially mounted linear guideways. In each case the serial mounting of the movable arm results in different inertial loads on the machine when the movable arm is displaced in different directions, due to the differing number of moving machine parts which must be displaced to enable such movement. Additionally, any force applied to the moveable arm, for example via the operating module, will result in bending moments being applied to at least part of the structure which supports the arm.
In an alternative form of coordinate positioning machine, the movable arm is supported by a plurality of members, each of which is connected to the mechanical earth of the machine, such as the table, for example. Machines of this type are known from e.g. International Patent Application Nos. WO91/03145 (Kearney & Trecker) and WO92/17313 (Geodetic Machines), in European Patent Application No. 534585 (Ingersoll), and U.S. Pat. No. 4,732,525, and typically include a movable arm, supported relative to a fixed, or "earthed" structure by means of a plurality of telescopic struts. Movement of the movable arm is achieved by extension and, where appropriate, contraction of one or more of the struts. A further type of coordinate positioning machine is shown in U.S. Pat. No. 4,976,582.